This invention relates to heat exchangers, and more particularly, to a flat tube for heat exchangers that may be made by forming an elongated strip. It also relates to heat exchangers utilizing such tubes and methods of fabricating the tubes.
Many heat exchangers in use today include so-called flattened tube which are variously described as flattened tubes and/or oval tubes. Many of these tubes include internal fins which divide the interior into a plurality of flow channels. These internal fins typically, but not always, provide pressure resistance to the interior of the tube by interconnecting opposed flat walls of the tube. They also increase heat transfer. In the usual case, the fin will be a much better heat conductor than the fluid passing through the tube with the consequence that the fin readily conducts heat from the fluid impinging against it to the side wall of the tube whereat heat exchange occurs with some other fluid.
A flat tube of this general type is disclosed in European Patent EP 646231. However, this type of tube is not particularly adapted for use in heat exchangers without headers or tube sheets. However, the tubes of the ""231 European patent are unsuitable for slitting and bending at their ends in order to provide intake funnels at the enlarged ends to input and avoid use of headers as disclosed in German Patent Application DE 100 16 113.8.
Other types of flat tubes are known. For example, in U.S. Pat. No. 4,805,693, a flat tube is disclosed which must be assembled from three different parts. The ends of the tube of the ""693 U.S. patent cannot be slit and bent to form an intake funnel because the part forming one flat side of the flat tube partially embraces or encloses the part forming the other flat side.
Still another flat tube is disclosed in European Patent Application EP 907062 and consists of two parts. However, this tube has no internal fin to form a number of flow channels in the interior of the tube and consequently, one must either insert an internal fin, leading to an increase in construction expense, or do without the advantages of internal fins. Similar drawbacks are associated with the flat tube disclosed in United Kingdom Patent 683161 of Nov. 26, 1952.
The present invention is intended to provide a flat tube that can be produced with cost effectiveness and can be slit and bent, if desired, on the ends so as to be employed in headerless heat exchangers and which may be additionally used in heat exchangers with headers and which includes an internal fin and provides the advantages thereof.
It is the principal object of the invention to provide a new and improved flat tube for use in heat exchanger and which contains an internal fin. It is also an object of the invention to provide a heat exchanger having such tubes as well as a method of producing such tubes.
An exemplary embodiment of the invention, in one aspect thereof, provides a flattened tube for use in a heat exchanger and which has two spaced relatively long side walls connected at their ends by two spaced relatively short end walls to provide a generally rectangular or oval-like cross section. An internal fin extends between the side walls within the tube to provide a plurality of internal flow channels within the tube. The invention contemplates the improvement wherein the tube includes two pieces, each including a corresponding one of the side walls, with at least one of the pieces including at least a portion of each of the end walls. A first of the pieces includes an integral, corrugated section defining the internal fin which is folded back into abutment with the side wall of the first piece. A second of the side pieces has its side wall abutting the corrugated section opposite of the side wall of the first piece. The pieces are sealingly bonded to each other at the end walls with the side walls of both the pieces being bonded to the corrugated section within the cross section of the tube itself.
In a preferred embodiment, at least one of the pieces includes a mating formation that mates with part of the other of the pieces to hold the pieces together during brazing. In this embodiment of the invention, it is preferred that the pieces be braze clad aluminum and that the bonding is provided by a braze joint.
One embodiment of the invention contemplates that both of the pieces have portions of the end walls and are bonded to each other at joints located noncentrally in the end walls with the cross sections of the tube being generally rectangular.
In the embodiment mentioned in the preceding paragraph, it is highly preferred that the joints be located closer to the second piece side wall than to the first piece side wall.
Another embodiment of the invention contemplates that the pieces are bonded together by joints located generally centrally of the end walls and that the end walls be outwardly convex to form a tube of oval-like cross section.
In one embodiment of the invention, the pieces are made of elongated metal strips and the end walls have a thickness double the thickness of the strips.
One embodiment of the invention contemplates that the pieces are bonded to each other by joints with the joints being defined by generally U-shaped formations on one of the pieces along with folded edges on the other of the pieces. Legs of the U-shaped formation abut the folded edges.
According to the invention, in another facet thereof, there is provided a heat exchanger including a pair of spaced header plates. Each of the plates has tube slots therein which are aligned with the tube slots in the other plate and a plurality of tubes made according to any of the preceding paragraphs and having opposed ends are disposed and sealingly bonded in the aligned ones of the tube slots.
According to still another embodiment of the invention, a heat exchanger includes a plurality of tubes made as stated above and aligned with their side walls facing each other in spaced relation. Serpentine fins extend between and are bonded to the facing side walls of adjacent tubes and the second piece of each tube, at its ends, has its end walls split and deflected away from the first piece of the same tube. The side wall of each first piece sealingly engages a deflected end of the second piece of an adjacent tube and a channel shaped tank is fit over and sealingly engages and is bonded to the deflected ends of the second pieces and the end walls of both of the pieces from the ends of the tubes to a location where the end walls are not split.
The invention, in still another facet thereof, contemplates a method of making a tube of rectangular or oval cross section and having an internal fin. The method includes the steps of (a) providing first and second elongated strips of good thermally conductive material, (b) forming the first strip to have a flat side wall section, two spaced tube end wall sections and a corrugated section disposed between the side wall section and one of the end wall sections, (c) bending the strip to bring the corrugated section into aligned abutment with the side wall section, (d) locating the second strip on the first strip in abutment with the corrugated section and with the end wall sections, and (e) bonding the second strip to the end wall sections in sealed relation and to the corrugated section.
According to one preferred embodiment of the method, step (d) is preceded by the additional step of forming the second strip into a generally central side wall section located between two end wall sections and step (d) is performed by abutting the second strip end wall sections with the first strip end wall sections.
The inventive method also includes, as part of a preferred embodiment, the sequence wherein step (b) includes the step of forming a second corrugated section between the first strip side wall section and the other of the first strip end wall sections and that step (c) is performed on both of the corrugated sections.
In a preferred embodiment of the invention, the forming of the first strip end wall section according to step (b) is accomplished by bending the strip at each edge of the side wall section to approximately a right angle thereto, and at an edge of each end wall section remote from the first strip side wall section, forming a reentrant tongue so that the reentrant tongue on each first strip end wall sections are directed towards each other.
Preferably, step (d) is preceded by the step of bending opposite edges of the second strip to form retention tongues directed toward the first piece end wall sections and step (d) includes fitting the retention tongues in interfering relation to the first strip end wall section prior to the performance of step (e).
This step may include lodging the retention tongues against the reentrant tongues in interference relation.
Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.